Functional Convergence of Listeria monocytogenes-Induced Monocyte Trafficking and Phagocyte-Borne Aluminium Redistribution: A Hypothesis on Motor-Compartment Exposure in ALS

Listeria monocytogenes induces directed monocyte recruitment to the central nervous system, dependent on IFN-γ and, in part, on CXCL9/CXCL10, with only a partial and transient contribution from CCR2. Aluminum-containing adjuvant particles, by contrast, undergo slow, phagocyte-associated redistribution dependent on CCL2/MCP-1, from muscle to distant organs, including the brain in low amounts — systemic biodistribution with occasional arrival at the brain, not necessarily a recruitment program to the nervous system equivalent to that of Listeria. These are distinct biological processes, with different evidentiary strength, magnitude and specificity. They could nevertheless converge functionally at phagocytic myeloid and neurovascular interfaces, not through a single molecular mechanism or a single type of cellular trafficking. This paper examines that functional convergence, distinguishes two modalities of Listeria-induced trafficking (bacterial transport and non-neuroinvasive CNS recruitment), describes the biodistribution of aluminum with the experimental precision it warrants, and directly addresses a problem usually left implicit in this type of hypothesis: that evidence of trafficking to the brain does not equate to evidence of access to the motor compartment — spinal cord, anterior horn, bulbar nuclei — which includes the principal anatomical territories affected in ALS. Also included, in its own section, is additional plausibility regarding direct aluminum toxicity to motor neurons, with its attendant caveats of source and interspecies dose equivalence.